Using semiconductor laser amplifiers (SLA's) as optical modulators, detectors, and multi-function network devices has recently received considerable interest in communications research. The use of an SLA as an optical signal amplifier is generally described by N. A. Olsson in "Lightwave Systems with Optical Amplifiers", Journal of Lightwave Technology, Vol. 7, 1989, pp. 1017-1082. In such use, the SLA amplifies relatively weak optical signals giving an strong output optical signal.
The use of SLA's as a simultaneous optical signal amplifier and detector has previously been described by A. Alping et al. in "100 Mbit/s Laser Diode Terminal with Optical Gain for Fiber Optic Local area Networks", Electronics Letters, Vol. 20, 1990, pp. 794-795, M. Gustavsson et al. in "Traveling Wave Semiconductor Laser amplifier detectors", Journal of Lightwave Technology, Vol. 8, 1990, pp. 610-617, and K. Koai et al. in Dual-Function Semiconductor Laser Amplifier in a Broadband Subcarrier Multiplexed System, IEEE Photonics Technical Letters, Vol. 2, 1990, pp. 926-928. In this application, the terminal voltage response of the SLA is electrically amplified and processed to detect information modulated on the optical carrier while it is being amplified.
An SLA has also been configured as an external modulator for data encoding with gain as described by U. Koren et al. in "High Frequency Modulation of Strained-layer Multiple Quantum-well Optical Amplifiers", Optical Fiber Communication Conference, OFC'91, San Diego, Calif., paper Th12, by G. Eisenstein et al. in "A Multiple Quantum Well Optical Amplifier/Modulator Integrated with a Tunable DFB Laser", International Conference on Integrated Optics and Optical Communications, Kobe, Japan, 1989, paper 19C2-3, and by G. Joyce et al. in "Wide Band Phase Modulation of a Semiconductor Amplifier", 16th European Conference on Optical Communication, 1990, paper TuF2.5. However, in the Koren and Eisenstein papers the quantum well SLA's were integrated with laser diodes and did not function as in-line optical amplifiers. In the Joyce paper, the SLA was used as a phase modulator and not as an intensity modulator.
For network applications, an in-line SLA that acts not only as a linear amplifier for the complete optical carrier but also as a simultaneous transmitter and receiver for selected channels is particularly desirable.